Air gaps in electrical machinery are required to be maintained within certain dimensional tolerances for proper operation. The tolerances are checked each time a rotor is changed, or when troubleshooting or testing. If the measured air gap is not within the required dimensional tolerance, then the air gap is adjusted to be within that range. Adjustment of the air gap to within the required dimensional tolerance helps improve commutation, regulation, physical clearance, among other machine parameters.
Contact methods such as a wedged feeler gauge type method have traditionally been used to measure air gaps. According to this method, a tapered bar or “wedge” (shown in FIG. 1 as 18) is coated with graphite and then slid between the core and the pole until resistance is felt. The wedge is then removed, and the point where the core and the pole scrape the graphite is measured. There are several problems with this method. The wedged feeler gauge type method is time consuming, cumbersome, and inconsistent. The method is prone to human error due to the varying amounts of force a person can use to push the wedge in. Obviously, pushing the wedge 18 in more or less yields a different air gap measurement. The measurement difference is significant especially since the air gap distance is small and the measurements are taken in micrometers. Additional variances in the measurement can result from the position on the rotor from which measurements are taken. The position on the rotor from which measurements are taken must be located under the exact center of the pole for an accurate minimum reading. Centering can be difficult in areas with limited visibility, and the pole's center must be aligned with a mirror. The method is also problematic because this method often requires the removal of internal bus work to get enough physical access to take the measurements. Unnecessary disassembly adds additional time and risk during reassembly.